Gunstar.
Its back. Its incredible and it will make you see that 2d is far far from dead. I played the original when it first came out and loved it.
Gunstar Super Heros takes that same formula. Revs it till it is way past the redline and cranks out 1000hp on your GBA. This game puts most other GBA action games to shame. Treasures programming skills are at full speed here. Huge bosses,paralax scrolling,hughe scrolling sprites,creative boss designs. Crisp animated charicters and explosions. Great play mechanics. Its everything Gunstar fans have ever wanted. If there was one negative point is that its not 2 players...but what are the odds you and a buddy both have the game and the same GBA(I use a DS)
Other than that this game easily gets a 9 out of 10.
Overall it is the most technically impressive and fun GBA game yet.